1. Field of the Invention
The present invention relates to a webbing retractor and, more particularly, to a webbing retractor which is arranged such as to reduce the pressure applied to the body of an occupant from a webbing when he has the webbing fastened.
2. Description of the Related Art
In seatbelt systems, a webbing is generally wound up onto a take-up shaft by rotating the shaft by means of biasing force from a spiral spring. The biasing force of the spiral spring is set so as to be relatively large, since it is necessary to fully rewind the webbing onto the take-up shaft after the occupant has unfastened the webbing. Accordingly, there has been the problem that the occupant may experience discomfort from the pressure of the webbing when he moves in the seat whilst driving with the webbing fastened.
To solve such problem, one type of webbing retractor has already been proposed wherein, when the occupant has the webbing fastened, the outer end of the spiral spring is wound up by the use of a motor in order to adjust the biasing force from the spiral spring, thereby allowing the webbing wind-up force to be adjusted to the optimum (see the specification of Japanese Utility Model No. 75129/1983).
However, the above-described type of conventional webbing retractor, which enables adjustment of the webbing wind-up force, suffers from the following problems. Namely, this conventional webbing retractor needs a webbing tension detector in order to adjust the webbing tension in accordance with the condition of the webbing, which changes depending on whether, for example, the occupant has the webbing fastened or not. In consequence, the structure and control of this type of conventional webbing retractor are complicated, disadvantageously.
In order to overcome the above-described disadvantages, the applicant of this invention has already proposed a webbing retractor (Japanese Utility Model No. 150083/1984) which has a simplified structure and involves a facilitated control operation. This improved webbing retractor is provided with a buckle switch which turns on when a tongue plate which is attached to one end of the webbing is engaged with a buckle device, so that, immediately after the buckle switch has turned off, the take-up shaft is activated by a motor so as to rotate in the direction in which the webbing is wound up.
However, the above-described webbing retractor, proposed by the present applicant, involves the following problems. Since the webbing is wound up by the operation of the motor immediately after the buckle switch has turned off, that is, immediately after the occupant has unfastened the webbing, the webbing is suddenly rewound by means of a relatively strong driving force from the motor which is abruptly applied to the webbing immediately after the webbing has been unfastened, and this may discomfort or shock the occupant.